Apparatus for the objective determination of the refraction of the eye



1935- v E. F. FINCHAM 2,012,758

APPARATUS FOR THE OBJECTIVE DETERMINATION OF THE REFRACTION OF THE EYE Filed Jan. 12, 1934 6'Sheets-Sheet 1 I LE v .50 Va a1 Zdf:

Aug. 27, 1935. E. F. FINCHAM APPARATUS FOR THE OBJECTIVE DETERMINATION OF THE REFRACTION OF THE EYE Filed Jan. 12, 1934 6 Sheets-Sheet 2 Aug. 27, E |N HAM 2,012,758

APPARATUS FOR THE OBJECTIVE DETERMINATION OF THE REFRACTION OF THE EYE Filed Jan. 12, 1934 6 Sheets-Sheet 3 F 1 .H/ m

0 A 5s :7 I Q I I 555 v a igw Aug. 27, 1935. E. F. FINCHAM APPARATUS FOR THE OBJECTIVE DETERMINATION OF THE REFRACTION OF THE EYE Fild Jan. 12, 1934 6 SheetsSheet 4 1935. E. F. FINCHAM 2,012,758

APPARATUS FOR THE OBJECTIVE DETERMINATION OF THE REFRACTION OF THE EYE Filed Jan. 12, 1934 6 Sheets-Sheet 5 65 I I f'z/l/enz vfi' 68 f j (law 1935. E. F. FINCHAM 2,012,758

APPARATUS FOR THE OBJECTIVE DETERMINATION OF THE REFRACTION OF THE EYE Filed Jan. 12, 1934 6 Sheets-Sheet 6 55 40 fjQ 1% LU 51 900 4, 45 g 35 [W Manx Patented Aug. 27, 1935 V. APPARATUS FOR; THE. oBJEo'rivn-nE'rER- MiNATION or THE aEFnAorroN-os'rini EYE Edgar Frank Fincham. Hornsey, London,

' 7 England .Applieation January 12, 1934, Serial No, 706,426

. r In Great L5 tiondens and a target orapertured diaphragm mounted between the lamp and lens.

In the simplest form of apparatus of thisicharacter lightafter passing the'lens is reflectedinto the subjects eye by a mirror or prism and-determination of the refraction is effected by adjusting the targetso as to give a sharp image on the retina. This image may be viewed .by means of some form of telescope. In this simple apparatus the accuracy. obtained depends upon the observ- .ers judgment of exact focus. I r

A further instrument of similar character designed to obviate the disadvantage mentioned uses the sameelements but the source of light is displaced slightly from the axis of the lenswhereas the observing system is placed upon the said axis This system is employed'to observe the image that has been produced on the retinaby the projection lens. All the light which enters the eye from the target does so through a decentred part of the pupil. If the target is placed ata point conjugate to the retina, its image upon the latter will be sharply focussed and will fell upon the axis whereas if it is-tooiar away or too near-the light will either cross the axis in the eye or will fail to reach it on reaching the retina and the image will be displaced toone side or the other. -udjustment is made bymoving the target along the ax s until the image on the retina is seen to disappear behind thelines of the target. The disadvantages of this instrument arethatit is difficult to judge exact coincidence betweenthe retinal image and the line on the target and that a considerable range exists between the disappearance of the image on one side of the target lines and its reappearance on'the othersideg The present invention providesimpmvedobjective apparatus which is similar to the last mentioned instrument in that'the source of'light is decentred from the axis of differs therefrom in that the target does not appear in the field of observation and hence does not mask the retinal image. I v

According to the inventionprovision is made of an instrument wherein the axis'of'th'e observing system is preferably on the axis of the eye but separate from the' common axis of the lens and target, the observing system comprising optic'al means such as prisms whereby the observed retinal image is divided intotwoormore parts shifted or reversed with respect to one another.

Britain January 24, 1933 22 Claims. (01. 88-20) r p v Thus if the imageis decentred to ,thel ri g ht the half .(assuming. the observed I forming part of the instrument but 7 extending across target into the eye observedreversed V image to be divided into two parts)... willbe decentred to thesame extent to the left; Correct setting is effected. when the image is, central and the two-observed halves are 'in alignment f'The accuracy in thisrr ethodis very high-because the effect of reversing, one half of "the to UNITED [STATE l E NT oF C ifY i v double the apparent efiect of anerroirlinltheset- 1 ting. In the accompanying illustrative draw n g'si Fig, 1 isa diagram of theoptical arrangement of the instrument. I

Fig. 2 is a planview,fpartlyin section, of aco n .venient constructional form of the instrument,

whilst I. Fig. 3 is a side elevation thereof and Fig. 4 is an end view, also partlyirisection.

Fig. 5 is an enlarged view partly cut-away showing-the target mechanism; Fig. 6 is a section on the line FigI'Z'is a'view similar toFig. 6 'showin aimo'dification oi an auxiliary target arrangement. f I

Figs. 8', 9 and 10 show in plan; side elevation and end view respectively,lanfloptical arrangement the observingsystem;

" Fig. 11 shows in side elevationa modified construction of scale reading mechanism. 1'

Fig. 12 is an underside plan view thereof, as

Fig. 13 is a 'section on theline of 3 Fig. 11.

Fig. 14 shows part sectionali plan. aiurther modification of the main and. targ'et arrangement whilst Fig- 15 is a cross; ,0: Fig. 14. l

Fig. 16 showsa modified former the ment shown in Figs. 14 m 15.1. Referring to .Fig..l, a represents. thefaxis of the observing telescope formed by the eyepiece'len'ses lilandlenseslland I V of the illuminated target l3 which i's'fmovable bei2, while I) represent the axis tween the limits or thepoints l3cand 131). "Light froma suitable source Mpassesthroughccmdensing lenses-l5 and a green, and is reflectedjliy, -a prism "111 through. a

slotted diaphragm get 13.

QThe light through theftarg i l3;

may consist'of a'slotted disc having a hair-line the slot, proceeds by wayfnf a proiectionlens" 9 to a rhornboid prismit which 18 and illurninateslthejtarit a the instrument. These prisms are The light emitted from the slotted diaphragm I 8 is slightly displaced from the axial line b of the target system, and the arrangement is such that 'with the target I3 placed at the normal or mid position shown in full lines, the light passing therethrough, after reflection by the rhomboid prism .20 forms an image'of thetarget f3 upon the retina, of the eye c, which image if. the eye is normal or emmetropic will lie upon the axial line a of the observing system II], II- and I2, but in other cases will lie to one side or otherrofthe said axial linep The image thus'formed upon the retina of the eye 0 is viewed by the observing system II), II and I2.

Situated between the eyepiece lenses I0 and the lens I I is ari'image-dividing arrangement 2| of prisms and refracting plates shown more particularly in Figs. 8, 9 and I0. This arrangement 2| comprises two parallel-sided plates of glass 22, 22a inclined with respect to the axis a and with eachlotherjand a pair o-fprisms 23, 24, the prism 24 having twice the heightpof the prism 23. Two further thin prisms 25 are arranged as shown to' "throughboth of the prisms 23and 2 s, the ulti.

mate eflect being that the two divided images are again-brought into line and appear as an unbroken image lat' d if the'eye is' emmetropic.

If .however'the light isdisplaced to either side by reason of the 'e'ye being myopic 'or'hypermetropic, asindicated by the line e, the light after refraction bythe plates 22, 22a entersthe prisms 23, 24 and emerges therefrom as two half images displaced from one another as shown at efand e The mergingoi the two halvesi's efiected byalter ing, thepositiofn' Qf-the'target I3 in order to bring the light image formed upon the retina of the eye 0 into register with the axi al line a of the observing system; The amount of displacement from the normal of the target I3 is a-measure in diopters of the refraction of. the eye 0 and the instrumentmay be calibrated accordingly.

The two thin prisms 25 are placedin the path of. the light image after it emerges from the prisms '23, 2'4 and serve to eliminate haziness of the image that occurs in the region of the point of division.

Referring] now .tofFig's; 2-6,' a preferred constructional form of instrument comprises a base 'plate. 26 having mounted thereon at one end the observingapparatusll and at the opposite end an adjustable chin -rest28 together-with a forehead rest-L29 which may be provided with adjustable side'pr temple pads 30,-

. The apparatus 2! is adjustably mounted as at' 31, 32 .to be movable in both lateral and longitudinal directions; while means such as shown'at 33 are provided for raising and lowering the 'apparatus. vTo permit of axial alignment suitable pivot and clamping means as shown at :34 are pro- I The observing telescope 35 containstheeyepiece lenses III], which are adjustablejby means of the knob IIla, together with the lenses I I and ll 'and forms the axis a of Fig. -1. ,The telescope 35'is rotatably mounted ma bracke't'36 fixed to the the telescope 35.

supporting means previously described and is arranged to be capable of rotation through an arc of. 180 to enable measurements to be made in diiferentjmeridians, and clamping means 31 in co-operation with a suitably marked sector plate 38 fixed to the telescope 35 serve to hold it in any desired position. r

Arranged parallel to the telescope 35, and secured thereto by brackets 39 is the target and illuminating tube 49 carrying at one end the rhomboid prism 20 andhaving at its opposite end a further tube at right angles thereto and serving to support alamp chamber 4 I. The lamp chamber 4 I carries the light source I 4, comprising an electric lamp, the filament of which is arranged to lie in line with the condensing lenses I5 housed in an adjustable manner in the tube 42. This tube 42 also carries the filter I5, prism I'I and slotted diaphragm I8.

The target I 3 (see more particularly Figs. 5 and 6)' is carried by a sliding tube 43 within the target tube and is arranged to-be adjusted as to posixtion by means of arack 44 secured thereto and 'extending'outwardly through a slot 45 in the tube 40; to engage a pinion operated by the knobs E25 A suitable pointer 48 (Fig. 3) is secured to the 'tube 43 and co-operates with a scale 49 secured to a housing 50 covering the rack and formed integral'with the tube 40;

For the purpose of fixing the accommodation of the eye of the patient, an auxiliary target 5I is arranged to move over approximately the same range as the target I3 and is formed as a small translucent disc carrying cross wires or other device, andadapted to be illuminated by light from the source "I4. The auxiliary target 5| is carried by an arm 52 extending outwardly through a slot 53 in'the tube 49 and terminates in a handle and guide-plate 54;

In order'to allow the passage of the auxiliary -target 5l. to bothsides of the target I3, a slot 55 is formed in the said target I3v and a slot 56 inthe wall of the tube 43 in register with the slot 53 in the wall of the tube 40.

Fig. 7 shows a modification of the auxiliary targetiarrangement wherein the tube 43 carrying themain target. I3 is divided into two parts, one carrying thetarget I3 and the other the auxiliary target 5| formed as a' translucent opening illuminated from behind bya separate source of light, the intensity of which can be controlled independently of that of the main source I4. In this-construction rack means similar to those previously describedimaybe used for adjusting the auxiliary target.

Figs. 11, '12 and 13 show amodified construction whereby both the scale of target movement and "the angleo'f rotation of thejapparatus 21 about the vaxis a; may be read from the eyepiece end of In this arrangement the telescope 35 is rotatably'mounted within a thick walled tube 51 forming partof the vmain supportingmember and taking the place of the :bracket .35. As previously described, the target tube 49 is arranged parallel to and carried by the telescope35, but in .this instance the tube 43 carrying the target I3 is arranged'to be connected to a stud 58 which extends outwardly through a slot 59 in the target tube? and terminates in a ring member 68.

The 'ring 6!! surrounds the tube 51 and is providedwith a scale SI. 'It'will be seen that .the

ring 69 rotates about the tube 5'! when the apscope 35 for viewing. it is preferredto use lenses of such power that 'eyepieces to secure The extra source of desired by a push-button.

the'bulb 12 passes through a diffusing of, the telescope 35,

target hereinbefore and in consequence the prism 63 is moved in accordance with the axial movement of ring 60 over a scale 61 provided on' the underside of the tube 51. g V

In operation'the scale. 6| indicating the angu-v lar setting of the apparatus is viewed by reflection in the prism 63" and is read in conjunction with an index line 68 engraved on the horizontal face of the prism. The .settingoi thetarget 13 causes the ring member lill tomove theprism carrier 62 along the tubei'5l'andzthe :scale' 61 is also viewed by reflection in the prism 63 and, is read in conjunction with a second index-line.- engraved on thehorizontal face of the prism.

Suitable means of illuminating the two scales may be employed, and if 1 desired a second eye,- p'iece' may be mounted below that of the tele:-

the scales in which case the adjusting knobsllla may be coupled to both simultaneous ,adjustment. light may .be controlled if Figs. 14 and 15 show a modified construction in which the target I3 is :in the form of across insteadoi a single hair line, the auxiliary target 'Bl being carried in a separate'tube I0 fixed t0 the outsideof the main target tube 40,.while the eyepiece ofthe telescope 35 with the optical system licarri'ed thereby :is arranged to be re.-

tated' about its axis'through an arc of 999.: The auxiliary target 5| is adjustableby meansof the knurled grip H and isfilluminated by a separate source of light, such as ,a small electric bulb [2 carried in a hinged mounti g .3-. The light from to illuminate the auxlliary'target 5|, the light emitted therefrom being reflected into the main target tube 40 by means of an adjustably mounted rhomboid prism 15.

. This modified arrangement is for the purpose 7 of allowing. easy determination oi the principal meridians of an-astigmatic eye, '1; e. the meridians of. greatest and least power respectively. .The

image of the'cruciform target upon theretina of the. pati'ents eye is and'for the measurement of the refractive power the line of the targetwhich is perpendicular to the planecontaining the axes of the illuminating and observing systems is ob- .served} by placing the eyepiece tube 35 containing the prism. system 2| in its original position 'so that this line is divided in its length.

vShould the instrumentbepositioned so tha the axes of the illuminating and observing 'systems do not lie 'upon one of'fthe principal meridians of an astigmatic eyeth'e' retinalj image will suffer an oblique displacement whichjcould not be ascertained in the image of the sirigle. =linje described with'reierenceto Figs. 2-7. In such case, however, the retinal image of the other targetli'ne, which lies exactly in the plane containingthe illuminating andiobserving systems, will be displaced fromthat. plane. Such a displacement is'ascertainedfby rotating the eyepiece tube and'the prisni 'systemthrOugh so that that'line of the image is nowfdiv'ided iniits length. and, due to the properties of the observing system, appears as a broken line. In

. lines;

medium 14.

viewed as before bymeans,

the practical use of this modified'form or the instrument itis adjusted'for, this observation'fir'st,

and'is rotatedin its br'acket 36until a position is will then lie in the planeoi one of theprincipal round 'in 'which'the image line 'use'd' for meridian 1 setting is seen to be unbroken... The instrument.

meridians of the eye. The eyepiece tube-and prism arrangement are thenrotated through 90".

in order'to allow the measurement eithe refraction to be made in that meridian; For the measurement of the refraction of theother princibracket 36.th1'ough 90.- In each position'of thezeyepiece and prism arrangement the line of the image not in use is eliminated by means of the two prisms 25.

Fig. 16 shows a modified form of the arrangement of Figs? '14 and 15 in which-"a T-shaped target 13 is used in conjunctionwitha rotatable pi e and prism system-" 2| mounted ec,- centrically of the axis. .of' the. observing tel scope'35t Y 7 pal meridian the instrument is. rotated in its In the arrangement shown in Figs. 14 and 15 and referring to the-"optical arrangement shown in Fig. 1 it will be apparent that when using the cruciform target it may be necessary .for-the 'li ght'therefromto-enter the eye 0 considerably d'ecentred in order to" retain a reasonable length of h'orizontaliimb on the right hand side of the cross (Fig. l5),'more particularly when the target I3 is in the extreme position l3b '(Fig. l.) ow- .ing to the loss caused by thetermination 1 of the reflecting surface of the prism 20', toperrnit the observation-of the retinal" image bylmearis ofthe i} In thearrangement shownin Fig. 16; the-vertelescope 35.

tical line of the target is used to'rneasure the rc fraction as previously described with the image;

dividingsystem Zl-in the position'shown" in full.

To determine-the principal meridians the f telescope eyepiece and system .2l are madecapable of rotation through QQiland owing toithe.

eccentric mounting thereof, the system 2.! and the point-of division of the viewed image caused by the two plates the horizontal limb of'the target as shown in chain dotted lines. r g

*I claim: '1. Apparatusfor the purpose set forth; :com-

prising a source'of light, a: lens, 'a' target mov- 22,-22a is swung across to bisect ably mounted between the said sourceand'lsns,

and anobserving system from the common axis said'obser'ving system including image-dividing means formed by a pair. of paralle'l-sidedglass co-operating prisms. I 7 ZJApparatus according to claim lyhaving. an additional pair of thin prismsat theiouter ends 'of the pair of prisms forming-part of .said imagedividing system.

having its axis separate 5 of the lens and target,

3; Apparatus for :the purpose. set forth, r eom; prising a source cf light, a lens, a target-between said source and lens, 'a' rhomboid prism to direct light from said target and lens intoa: patients eye at adecentred part thereofjand anobserving'system having its axis separate from the'come mon axis of the lens and targetand comprising image-dividingprismsu i 4. Apparatus for the purpose set comprising a source of light, a lens; a target movably mounted between said source and-lens, said-target producing "a cruciformimageon the retina of a patients eye; and an observingsystem having 7 its axis separate from the common-- axis :of -the plates at an angle to one another and a pair of. r

adjustment whereby the principal target producing a IT-shaped image on the retina of-a patients eye, and an observing system hav? ing its axis separate :fromthe'common axis ;of thelens and target, said observing system com? prising means for dividing 'said image'intotwo relatively reversed parts and being provided with an adjustmentwherebythe principal meridians of an astigmatic eye may her-determined.

6. Apparatus for the purpose set forth comprising a base plate, an adjustable supportcarried by said base, an:observing system angular -ly adjustable on said support for inspecting the retina of an eye through a single, area of the pupil thereof, said observing system comprising an eyepiecej and an image-dividing, arrangement, and an image-producingsystem for produ'cingan image of. a target upon, the retinacarried'by said observing system comprising a source of light, alens, a prism,'and a targetmovably mounted between said lens'and 'source, the' commonaxis of said lens and-.target being separate from the axis of the observing system.

7. Apparatus for the purpose set forth-comprising a base, a pillar adjustable onsaid base,

anobserving system journalled on said pillar, said system including an eyepiece and an image-dividing arrangement, a tube carried by said observ ing system and itself-carrying a source of light at oneend and, aprism at the other end, the

axis of said tubebeing parallel to-the axis of the observing system, and a lens and target axially mounted within saidtube, said targetbeing provided with means extending externally of the tube for adjusting itsposition .with relation to thelens,

' 8. Apparatusaccording'toclaim '7 having on the base-plateia patients head-rest. 1 e

9. Apparatus for the purpose set forth, comprising a base, a; pillar adjustable on saidbase, an observing system journalled on said pillar, said system including anreyepiece and anirnagedividing arrangement, ,a tube carried by said observing system anditself carrying a source of light atone end and a'prism at the other end, the axis of said tube being parallel to the axis of the observing system, a glens fixed axially within said tube, a target movably mounted within said tube, means extending externally of the tube for adjustment of the positionof said target, andmeans'for indicating theadjustment of said target. j

prising a, base, a pillar adjustable on saidgbase, an observing system journalled on said pillar,

said system including an eyepiece and an image- 10. Apparatus for the purpose set forth, comdividing arrangement, a tube carried by saidobserving system and itself carryinga source, of light at' one end and a prism at'the-jother, end,

the axis of said tube being parallel to the-axisof the observing'system, a lensfixed axially within 7 said tube, a main target in said tube adjustably mounted-with relation; to said lens, an auxiliary target 'similarlyadjustable within a said tube, and means extending externally of thehousingfor independent adjustmentiofrsaid targets.

11'. Apparatus for the purpose set forth, comprising a sourceof light, a targetilluminated by 7 atively reversed parts.

aoravas :said source, optical means for transmitting an image. of said target .to the retina of an ,eye, means for observing said image on the ,retina through a single area of the pupil of said eye, and means associated with said observing means for dividing theretinal image for observation into i "at least twof'parts reversed one with respect to means for observing ,said image ,on the retina,

through'a single :area of the pupil of .said eye,

land means associated with said observingmeans- :for dividing the retinaltimage for observation into atleast two relatively reversed parts.

13; Apparatus for the purpose set forth, hav-- ing an illuminatingsystemcomprising a source of 'light,-a lens, and .atarget mounted between the said source and lens, said lens forming an image ofsaid target on the retina of the patients eye,

means for observing said image through a single area of the pupil of .said eye,-said me'ans'including image-dividing means, and a journal'bearing whereby the illuminating" system andobserving means may be adjusted about the axis of the said -obs'er'vingmeans; I e 14. Apparatus for the purposeset forth, having-an illuminating systemcomprisingla source of light, a lens, a target between 'said source and lens, and a color filter, said lens producing an image of said target on the retina of a patients eye, and an observing systemincluding means for dividing the observed retinal image into-at least two relatively'reversed parts.

' #15. Apparatus 'forthe purpose set forth,com-

prising a source of light, a main target, an auxil iary target-mounted so" asto be movable independently of the maintarget, said two targets being illuminated by said source, optical means for transmitting images of said targets to the retina of a patients eye, and an observing system comprising means whereby the'retinal image of the main target is divided into at least two rel- 16. Apparatus for the purpose set forth, comprising a source oflight, a lens, a target movably mounted" between said source and lens, said lens producing an image of said target on the retina;

of the eye under test'jand an optical system for observing said image through a single area of the pupil of said eye, said system comprising'imagedividing means and a screen having 'den'ot ations for determination of the meridian of observation. 17. Apparatus vfor the purpose set forth, having an illuminating system comprising a source of light, a lens, and a targetmounted between said source and lens, said system producing an image of saidtarget on t'he retina of "the eye ,under test, means for dividing said image for observation into. two reversed parts, an observing 'pef, and optical'means whereby at least one 5 6f the relative "settings of the'target and lens can be read at saidleyepiece.

' 18, Apparatus for the purpose set'forth, comprising, a source of light, a target, means for jforming anlimage of saidtarget on the retina .of an eye under test, viewing meansadapted to allow observation of said image through a single area. of the pupil of said eye and along an axis inclined inone plane to the axis of the beam of light within the said eye produced by said imageiorming means, means for causing said axes to intersect on the retina, and an optical device associated with said viewing means to divide the said image into two parts reversed one with respect to the other.

19. Apparatus for the-purpose set forth, comprising a source of light, a target, means for forming an image of said target ,on the retina of an eye under test, viewing means adapted to associated with said viewing means to divide thesaid image into two parts reversed one with respect to the other.

20. Apparatus for the purpose set forth, comprising a source of light, a target, means for forming an image of said target on the retina of an eye under test, viewing means adapted to allow observation oisaid image through a single 1 area of the pupil of said eye and along an axis inclined in one plane to the axis of the beam of light within the said eye produced by said image' forming means, said target including aline lying in said plane, means for causing said axes to intersect on the retina, and an optical device associatedwith said ,viewing means todivide the;

said image into two parts reversed one with re spect to the other.

21. Apparatus-for the purpose set forth, com 7 prising a source of light, a target, means for, forming an image of: said target on the retina" of an eye under test, viewing means adapted to, allow observation of said image through'a sin gle area of the pupil of said eye and'along an axis inclined in one plane to theaxis of the beam of 10 light within the, said eye produced by said image!- forming means, means for causing said axes to intersect on the retina, and an optical device asi sociated with said viewing means to divide the said image along a line parallel to said plane into 15' two parts reversed one with respect to the other.

22. Apparatus for the purpose set forth, comprising a source of light, a target, means for forming an image of said target on theretina of an eye under test, viewing means adapted to al- 7 low observationof said image through a single 7 area of the pupil of said eye and along an axis inclined in one plane to the axis oi the beam of light within the said eye produced by said imageforming means, said target including a line at an 25 angle to said plane, means for causing said axes to intersect on the retina, and an optical device associated with said viewing means to divide the 5 said image alonga line parallel to said plane into 7 two parts reversed o c with respect to the other. 0

EDGAR F. FINCHAM. I 

